Burr-free shaped charge perforating



Jan. 30, 1968 R. 5. HICKS 3,366,18

BURR-FREE I SHAPED CHARGE PERFORATING Filed June 28, 1965 INVENTOR.

ROY G. HICKS' ZM/ZW ATTORNEY United States Patent 3,366,188 BURR-FREE SHAPED CHARGE PERFORATING Roy G. Hicks, Houston, Tex., assiguor to Dresser Industries, Inc., Dallas, Tex., a corporation of Delaware Filed June 28, 1965, Ser. No. 467,429 2 Claims. (Cl. 1754.6)

ABSTRACT OF THE DISCLOSURE An auxiliary metal plate is positioned between the shaped charge and the casing Wall, the outside diameter of the semi-cylindrical plate being substantially equal to the inside diameter of the casing. The shaped charges are embodied in both capsules and hollow carrier guns.

This invention relates to shaped charge perforating apparatus and more particularly to a new and improved method and apparatus for producing burr-free shaped charge perforating in oil field casing.

It has become common practice in the completion of oil and gas wells to perforate the well casing to bring the well into production by the utilization of detonating explosives of high velocity and of the general character and form known as shaped charges as, for example, the type disclosed by US. Patent No. 2,399,211 to C. 0. Davis et al., issued Apr. 30, 1946.

In order to locate the shaped charges opposite the proper strata, the shaped charges are assembled into a gun which is lowered into the well. The guns used for shaped charge perforating are basically of two types. One, known as the hollow carrier gun, is comprised of a hollow tube containing a plurality of shaped charges, such gun being retrievable after the shaped charges have been fired and thus reuseable for a number of times. A common form of such gun is disclosed in US. Patent No. 2,494,256. The other type of gun, which has been used particularly in smaller tubing, is the capsule type in which each individual shaped charge is encased in its own pressure container and mounted in a carrier. This type of gun is disclosed in US. Patent No. 2,629,325.

Although it has been found that the depth of penetration resulting from the detonation of a shaped charge in many types of formation is often times greater than the depth of penetration obtained from a projectile, it has been determined that when a shaped charge is used a ragged burr is formed around the perforation in the inside wall of the casing. The burr may cause difiiculties in subsequent completion operations. This is particularly true when packers, plugs and other tools that have small diametral clearance between themselves and the inside wall of the casing are run. Burr-free perforations also eliminate difiiculties encountered in obtaining a seal when using a ball to seat and seal perforations for the purpose of selectively fracturing, acidizing or stimulating the formation.

Accordingly, it is the object of the present invention to provide novel method and apparatus for obtaining burrfree shaped charge perforations.

It is another object to provide a novel shaped charge perforating apparatus which will produce a burr-free perforation.

It is a further object to provide a novel method whereby a burr-free shaped charge perforation of a casing may be obtained.

It is still a further object to provide a shaped charge perforating gun having an auxiliary portion which will cooperate with shaped charge to eliminate the burr in the perforation.

These and other objects and advantages of the invention which will more clearly appear from the detailed description which is about to follow are accomplished in a capsule-type shaped charge gun 'by having an auxiliary member positioned in front of a capsule shaped charge and then having means which will urge the auxiliary member against the wall of the casing whereby the capsule-type charge will shoot through the auxiliary member before contacting the wall of the casing. It has been found by utilizing such apparatus that the perforation resulting from the discharge of the shaped charge is burr-free and chamfered.

The invention will be described with more particularity with reference to the drawings in which:

FIG. 1 is a cross sectional view of a portion of an oil field casing having a shaped charge perforation in which there is a burr formed around the perforation.

FIG. 2 is a view similar to FIG. 1 showing a burr-free shaped charge perforation in accordance with the present invention.

FIG. 3 is a vertical section View of a portion of a bore hole in which there is an exemplary embodiment of the novel shaped charge perforating apparatus of the present invention.

FIG. 4 is a transverse section view taken generally along lines 4-4 of FIG. 3.

FIG. 5 is a view similar to FIG. 3, showing the invention applied to a hollow carrier gun.

Referring now to the drawings, it can be seen that FIG. 1 illustrates a portion of a section of oil field casing 8 which has a perforation 10 formed by the detonation of shaped charge. Surrounding the perforation 10 there is a ragged burr 12 on the inside wall of the casing 8, the wall which faced the shaped charge, and a second burr 13 on the outside wall. The burrs 12 and 13 are probably formed by the reaction of the metal to the jet from the shaped charge. In other words, as the force of the jet struck the metal, the molecules in the metal moved away from the main stream of the jet. In so moving, they bunched up around the circumference of the jet, thereby forming the ragged burrs 12 and 13.

FIG. 2 is a section of oil field casing 8 similar to that shown in FIG. 1 in which there is a perforation 14 formed by the method and apparatus of the present invention. It is to be noted that perforation 14 has no burr around its circumference on the inside wall of the casing 8. Instead there is a burr 17 formed on a piece of metal 15 which was positioned against the inside of the casing 8 and which received the initial blast from the shaped charge. The perforation 14 does have a burr 13 on the outside of the casing similar to FIG. 1.

As has been previously mentioned, one of the disadvantages of shaped charge perforating of oil field casing is the formation of the burr around the perforation on the inside wall of the casing. This burr is undesirable and is the cause of difficulties encountered in subsequent operations in the well bore. It has been found that one method of eliminating the burr is to position an auxiliary member between the shaped charge and the inside wall of the casing. It appears that the jet from the shaped charge slams the auxiliary member into intimate contact with the inside wall of the casing and acts as an anvil preventing the formation of the burr on the inside wall of the casing. Accordingly, it has been found that by firing a shaped charge through an auxiliary member positioned against the inside wall of the casing, the perforation that results is burr-free on the inside of the casing.

Referring now to FIG. 3, there is shown the novel shaped charge perforating apparatus 16 of the present invention, located in a well bore 18 having a casing 20. It can be seen that the perforating apparatus 16 is formed of a plurality of capsule type shaped charge units 22 which are attached to a carrier strip 24. One means of attaching the shape-d charge units 22 to the carrier strip 24 is to provide the carrier strip 24 with a number of raised tabs 26. The shaped charge units 22 are then attached to the carrier strip 24 by means of wires 28 which are attached to the rear portion of the shaped charge units 22. Other means of attaching shaped charge units to a carrier strip may be utilized by those skilled in the art.

Spring members 30 are attached to the bottom and top of the carrier strip 24 to urge the apparatus 16 against the inside wall of the casing 20 whereby the carrier strip is in intimate Contact with the inside wall of the casing 20.

The apparatus 16 is provided with means attaching it to a customary cable head and easing collar locator 32 which, in turn, are attached to the cable (not shown) for raising, lowering and positioning the apparatus 16 in the well bore 18, as is well known in the art. Customary ignition means such as Primacord 34 may be utilized to detonate the various shaped charge units 22.

The shaped charge carrier strip 24 has an arcuate configuration in cross section having an outer circumference 36 which in general matches the inner circumference of the casing. This can best be seen in FIG. 4. Although the outer circumference 36 of the carrier strip may not exactly match the inner circumference of the casing 20, it is desirable that the two members mate fairly close. The action of the jet from the shaped charge will tend to force the outer wall of the carrier strip 24 into intimate contact with the inner wall of the casing 20. It has been found for five inch or five and a half inch outside diameter casing, having an inside diameter running roughly from four and a quarter to five inches, the outside radius of the carrier strip may be in the neighborhood of two and a quarter inches. With such relationship, it has been found that there is an intimate mating upon the discharge of the shaped charge unit and that the carrier strip acts as an anvil and prevents the formation of the burr on the inside wall of the casing.

It has also been found desirable to use a carrier strip having a thickness of approximately one eighth of an inch. By using a strip of this thickness, it has been found that the burrs on the inside wall of the casing are eliminated and that there is a minimum expenditure of energy lost by the shaped charge in going through the strip. If a substantially lighter strip is utilized, it has been found that the burrs will not be eliminated. If a substantially heavier strip is used, while the burrs may very well be eliminated, the energy of the shaped charge used in going through the strip will substantially reduce the depth of the penetration in the formation, such reduction being highly undesirable. Therefore, by using a strip having a sufficient body to act as an anvil to prevent the formation of the burrs and at the same time being of such thickness that there is not an excessive amount of force dissipated by the energy of the shaped charge in penetrating it, a burr-free perforation is obtained and at the same time the depth of penetration is not materially decreased.

FIG. illustrates the invention applied to a hollow carrier type gun 42. Located in the hollow carrier gun 42 are a plurality of shaped charges 44, Attached to the hollow carrier gun 42 are anvil members 46. Springs 48 may be used in attaching the anvil members to the gun 42. The springs 48 will keep the anvil members 46 in intimate contact with the inside wall 50 of the casing. The form shown in FIG. 5 operates in similar manner to the capsule type gun shown in FIG. 3. The jets from the shaped charges 44 first strike the anvil members 46 and force anvil members 46 into intimate contact with the inside wall 50 of the casing. By such action the initial energy of the blast is absorbed by the anvil members and the anvil members also act to prevent the formation of a burr around the perforation on the inside wall of the casing.

In summary it has been found that by positioning an anvil member between the shaped charge and the inside wall of the casing, the burr on the inside wall of the casing customarily resulting from a shaped charge perforation is eliminated and the edge of the perforation is in effect chamfered. Such perforations will not interfere with subsequent operations in the well bore and will materially aid in forming a seal for walls should perforations require sealing in subsequent fracturing, acidizing or stimulating operations.

I claim:

1. Shaped charge perforating apparatus for perforating casing in a well bore comprising:

(a) at least one shaped charge unit;

(b) means for detonating said at least one shaped charge unit;

(c) hollow carrier means for positioning said at least one shaped charge unit within a well bore, said at least one shaped charge unit being positioned in said hollow carrier means;

(d) anvil means positioned exterior to said hollow carrier means, whereby said anvil means can be positioned between said hollow carrier means and the casing of the well bore, said anvil means having an arcuate configuration with the outer circumference thereof conforming substantially to the inner circumference wall of the casing; and

(e) spring means for urging the anvil means toward the casing, whereby the anvil means receives the blast from said at least one shaped charge unit upon detonation prior to the well casing receiving said blast.

2. The apparatus according to claim 1 wherein said anvil means has a thickness of approximately one-eighth inch.

References Cited UNITED STATES PATENTS 2,587,244 2/1952 Sweetman 4.6 2,616,370 11/1952 Foster 1754.53 2,879,972 3/1959 Porter 175-4.6 X 2,952,319 9/1960 Popham l66-35 3,089,416 5/1963 Gilbert 1754.6 3,147,807 9/1964 Whitten 16655.1 X 3,268,016 8/1966 Bell 1754.51

CHARLES E. OCONNELL, Primary Examiner,

DAVID BROWN, Examiner, 

